1. Field of the Invention
The present invention relates to non-reciprocal circuit elements, communication devices, and methods of manufacturing the non-reciprocal circuit elements.
2. Description of the Related Art
Non-reciprocal circuit elements for lumped-constant isolators used in mobile communication devices, such as cellular phones, generally have a function for transmitting signals in one direction and preventing the transmission in the other direction. A non-reciprocal circuit element comprises a permanent magnet, a center electrode assembly including a ferrite and a plurality of center electrodes disposed on the ferrite. The magnet is disposed in a region defined by a metallic component and the center electrode assembly is disposed in a region defined by a resin component combined with the metallic component.
FIG. 20 is a plan view of a resin component 3. The resin component 3 is combined with a lower metallic component 4 to form a case. A bottom 3a of the resin component 3 is provided with connection electrodes (an input-lead-out electrode 14a, an output-lead-out electrode 15a, and an intermediary electrode 17) electrically connected to center electrodes. The bottom 3a has windows to define a first cell 3c and second cells 3d, and the lower metallic component 4 is exposed in the first and second cells 3c and 3d to serve as grounding-lead-out electrodes 4a. One grounding-lead-out electrode 4a exposed in the first cell 3c which is in the center of the bottom 3a is electrically connected to a grounding electrode of the center electrode assembly. The other grounding-lead-out electrodes 4a exposed in the second cells 3d are electrically connected to electrical functional components such as matching capacitors. These connections are ensured by, for example, a soldering paste 60. The soldering paste 60 is applied to the electrodes 4a, 14a, 15a, 17, and the like with a dispenser. The soldering paste 60 may consist essentially of Snxe2x80x94Sb, Snxe2x80x94Pb, or Snxe2x80x94Ag, for example. The surface color of the soldering paste is gray.
The lower metallic component 4, which serves as the grounding-lead-out electrodes 4a, and the connection electrodes 14a, 15a, and 17 are formed by nickel plating (typically 1 xcexcm thick) and silver plating (typically 4 xcexcm thick), in that order, on base iron. The surface color of the electrodes 4a, 14a, 15a and 17 is silver.
The resin component 3 is formed of a liquid crystalline polymer. Liquid crystalline polymers are originally white, but the polymer used for the resin component 3 contains a black colorant in order to hide dirt thereon.
Mobile communication devices are increasingly required to be small and inexpensive and to have improved reliability in use. Hence, isolators, or non-reciprocal circuit elements, used for the communication devices also must be small and inexpensive, and have improved reliability. Accordingly, the electrical functional components and the resin component 3 included in the non-reciprocal circuit elements are required to be small.
Unfortunately, if the resin component 3 and the electrical functional components are directly miniaturized, the miniaturized resin component 3 and electrical functional components are likely to cause soldering problems at the connection electrodes 14a, 15a, and 17 and at the electrodes of the electrical functional components. For example, the use of too little soldering paste 60 is liable to cause an open circuit at the connection electrodes 14a, 15a, and 17 and matching capacitors. Also, the use of too much soldering paste 60 (see the soldering paste 60 applied on the connection electrode 15a in FIG. 20) is liable to cause a short circuit because the soldering paste 60 comes into contact with undesired areas.
In order to prevent any open circuit and short circuit in the non-reciprocal circuit element, the soldering paste 60 must be applied to the connection electrodes 14a, 15a and 17 and electrodes of the electrical functional components while being controlled within a predetermined range. Controlling the amount of soldering paste 60 becomes increasingly important according to the miniaturization of the non-reciprocal circuit element. For controlling the amount of soldering paste 60, visual examination and image analysis may be performed. However, visual examination is inefficient, and therefore is not suitable for mass production.
In contrast, image analysis is efficient and suitable for mass production. Generally, exposing an object to visible light causes reflection, at the surface of the object, having an intensity in proportion to the light reflectance of the object. The intensity of the reflection is determined by an image pickup tube, and an output of the image pickup tube can be processed to form an image. In this image, a white image represents an area causing a strong reflection and a black image represents an area causing a weak reflection. In other words, when an object is exposed evenly to a substantially constant visible light, an area forming a white image has a high light reflectance and, in contrast, an area forming a black image has a low light reflectance. In this image analysis, the image is binarized according to two levels which indicate black and white, respectively, and thus the amount of soldering paste 60 is determined according to the binarized image.
However, if the threshold for the black-and-white binarization is set between the image formed by the reflection at the soldering paste 60 and the images formed by the reflections at the connection electrodes 14a, 15a, and 17, the soldering paste 60 and the resin component 3 are not distinguished from each other.
More specifically, the reflections at the connection electrodes 14a, 15a, and 17 are the strongest, the reflection at the soldering paste 60 is the second strongest, and the reflection at the resin component 3 is the weakest because surface colors of the connection electrodes 14a, 15a, and 17, the soldering paste 60, and the resin component 3 are silver, gray, and black, respectively. Therefore, if the threshold for the binarization of the image is set between the image formed by the reflection at the soldering paste 60 and the images formed by the reflections at the connection electrodes 14a, 15a, and 17, the soldering paste 60 and the resin component 3 are not distinguishable from each other. Hence, it is impossible to detect when soldering paste 60 is spreading to the connection electrode 15a, nor consequently can it be determined whether the soldering paste 60 is applied within a predetermined range.
For a solution of this problem, it has been suggested that two thresholds be set. A first threshold is set between the image formed by the reflection at the resin component 3 and the image formed by the reflection at the soldering paste 60, and a second threshold is set between the image formed by the reflection at the soldering paste 60 and the image formed by the reflections at the connection electrodes 14a, 15a, and 17. Thus, the soldering paste 60 can be distinguished from the connection electrodes 14a, 15a, 17 and the resin component 3. However, this solution requires an expensive image analyzer and therefore leads to expensive non-reciprocal circuit elements.
Accordingly, the present invention provides a miniaturized, inexpensive, and reliable non-reciprocal circuit element and communication device and a method of manufacturing the non-reciprocal circuit element.
To this end, according to one aspect of the present invention, there is provided a non-reciprocal circuit element comprising:
a metallic component,
a resin component combined with said metallic component,
a ferrite,
a permanent magnet, which applies a DC magnetic flux to the ferrite, and
a center electrode assembly comprising a plurality of center electrodes which are disposed on the ferrite, wherein:
the resin component accommodates the center electrode assembly,
the resin component has connection electrodes which are connected to the center electrodes by solder,
the metallic component accommodates the permanent magnet and the center electrode assembly, and
respective light reflectances of both the connection electrodes and the resin component are higher than that of the solder.
Preferably, the color of the resin component is white or non-black so that the light reflectance of the connection electrode is the same as or higher than that of the resin component, and the light reflectance of the resin component is higher than that of the solder, or the light reflectance of the resin component is higher than that of the connection electrode, and the light reflectance of the connection electrode is higher than that of the solder.
In other words, the color of the resin component is preferably white or non-black so that the light reflectance of the resin component is higher than that of the solder.
The present invention is further directed to a non-reciprocal circuit element in which both a light reflectance of the connection electrodes and a light reflectance of the resin component are lower than that of the solder.
In another aspect of the present invention, a method of manufacturing a non-reciprocal circuit element includes a step of applying a predetermined amount of soldering paste to each of predetermined positions on connection electrodes in a resin component, a step of determining the amount of soldering paste applied to each connection electrode with an image analyzer, and a step of disposing a center electrode assembly on a predetermined position in the resin component and connecting the center electrodes with the connection electrodes with the solder paste.
The invention is further directed to a method of manufacturing a non-reciprocal circuit element in which both a light reflectance of the connection electrodes and a light reflectance of the resin component are either higher or lower than that of the solder.
In another aspect of the present invention, a method of manufacturing a non-reciprocal circuit element includes a step of applying a predetermined amount of soldering paste to each of predetermined positions on connection electrodes in a resin component, a step of determining the amount of soldering paste applied to each connection electrode with an image analyzer, a step of disposing electrical functional components on predetermined positions in the resin component, a step of applying a predetermined amount of soldering paste to each of predetermined positions on the electrodes of the functional components, a step of determining the amount of soldering paste applied to each electrode of the functional components with an image analyzer, and a step of disposing a center electrode assembly including center electrodes on a predetermined position in the resin component and connecting the center electrodes of the center electrode assembly with the electrodes of the electric functional components with a soldering paste.
Further, the light reflectance of the connection electrodes and resin component respectively are higher than that of the soldering paste, and the threshold for the black-and-white binarization is set between the image formed by the light reflectance of the solder paste and that of the connection electrodes and resin component. Thus, the solder paste can be distinguished from the connection electrodes and the resin component.
In addition, in the same way, the solder paste can also be distinguished if the light reflectances of the connection electrodes and resin component respectively are lower than that of the solder paste.
Preferably, the resin component is formed of a colorant-free resin. By not needing to add colorant to the resin, the manufacturing cost of the resin component can be reduced.
Preferably, the resin component is formed of a material selected from the group consisting of liquid crystalline polymers, polyphenylene sulfide, and poly (ether-ether-ketone). These materials are thermostable and have low dielectric loss factors.
Preferably, the connection electrodes are coated with silver, which has a high conductivity. Thus, the insertion loss of the non-reciprocal circuit element can be low. In addition, the use of silver leads to rustproof and solder-wettable connection electrodes.
The non-reciprocal circuit element may further comprise matching capacitors. In this instance, preferably, the surface material of the capacitor electrodes is the same as that of the connection electrodes. Thus, the thresholds for the determination of the amounts of soldering paste applied to the connection electrodes and that applied to the electrodes of the capacitors can be set at the same value, and therefore process control can be facilitated.
Preferably, the amounts of soldering paste are determined according to reflected images which are binarized by a monochrome image analyzer. Since monochrome image analyzers are inexpensive, the cost of the manufacturing facilities can be reduced and therefore the manufacturing cost of the non-reciprocal circuit element can be reduced.
Also, the present invention is directed to a communication device comprising a non-reciprocal circuit element described above. In the communication device, problems such as open circuits and short circuits due to miniaturization of a non-reciprocal circuit element can be prevented with low cost, small-sized, and high reliability.